Re: Duration of rank
I heard a prominent student of a famous shihan closed her dojo after an illness caused her to lose her technical abilities. That was her choice. Loss of skills didn't cost her rank, but it did cost the ability to run a dojo in her eyes. Students are even promoted post-humously, so even being dead does not cost a person rank or their ability to be promoted.
I have heard of requests to remove a person's rank because of criminal activity. This can get you thrown out of a particular dojo or association but rank (and really the skills acquired) stay.
That said, if I didn't train for years, everyone I trained with initially will have either quit or continued on - either stopped or continued to improve. If someone was a lower rank when I left, they are a higher rank now and deserve to be treated by me as such. Testing standards and preferred variations will have changed, and I would have possibly forgotten the ones I ever knew anyway. I should expect to be treated as a low skilled guest by the white belts. There should be no chance that I could teach, no pearls of wisdom being offered by me to any training partner. I might not be physically fit enough to take the advanced classes. And that's just if I returned to my own association - if I took years off to start again in another association, all the ghostly memories of techniques might be completely different than what the teacher wants.
The rank is there, but demanding the respect and perks of rank would be a poor choice.